Response to Not Soy Fast

More details on every topic below, as well as many others, can be found in the companion article to this piece, Soy: What’s the Harm?, just published on VeganHealth.org. The reference numbers in the article below link to the references of Soy: What’s the Harm?

I approached each subject regarding soy without a foregone conclusion, trying to get to the truth rather than putting a positive spin on the results. While I think there is a limit on how much soy is safe to eat each day, that limit has not yet been determined. There is a great deal of evidence, however, that unless you have thyroid issues or are allergic to soy, two servings per day is perfectly safe.

I want to give special thanks to Jean Bettanny for her careful editing of Soy: What’s the Harm?

In her article, Not Soy Fast, Kristin Wartman argues that “…the research is mounting that soy foods are not only questionable in terms of their benefits, but in fact, may be hazardous to your health.”

Wartman describes the Cornucopia Institute’s recent report in which they describe finding residues of hexane in some soy food ingredients. The Cornucopia Institute gave few details about how much hexane they actually found and there is no evidence that the amounts typically found in soy foods are harmful to consumers. However, in the interest of worker and environmental safety, as well as trying to limit any potential harm from hexane residues, I cannot fault anyone for avoiding soy products produced with hexane. As Wartman points out, there are companies that make alternative meats without using hexane, such as Tofurky and Field Roast. (Also see Hexane in Soy Food and Do Veggie Burgers Contain Hexane?)

But this is where Wartman and I part ways. While there are legitimate concerns regarding soy, Wartman cherry-picked the studies and ignored the vast majority of research. For the topics in this article, I will cover the full range of research findings, both pro and con.

A little background: Soy contains isoflavones which have the ability to bind to estrogen receptors and can affect thyroid hormone (especially if someone has iodine deficiency). There are about 25 mg of isoflavones in one serving of soy.

Breast Cancer

Wartman implicates soy as a cause for breast cancer, mentioning only one study. Unfortunately, she didn’t cite the study correctly, so it is not clear to which she was actually referring. In any case, here is a run down of the research.

Case-control studies on soy and breast cancer have been generally encouraging to those with soy in their diets, with about half associating soy with a lower risk for breast cancer and the other half showing no effects.

Prospective studies, which are generally a higher level of evidence than case-control, have also been very positive. Of the six studies done on populations with higher soy intakes (about one to two servings per day is the typical upper intake amount), the Singapore Chinese Health Study (21), the Shanghai Women’s Study (22, 23), and the Japan Public Health Center study (26) all found that higher intakes of soy were associated with a reduced risk. The Japan Collaborative Cohort Study (17) and the Japan Life Span Study (30) found no association. The European Prospective Investigation into Cancer-Oxford (24), which contained a large number of vegetarians, also found no association. Regarding the lack of association in the European study, some have speculated that in order to receive benefits from soy, exposure must occur during adolescence when breasts are developing, while Western vegetarians often adopt the diet as adults.

As for women with breast cancer, including those with tumors that grow in response to contact with estrogen (known as estrogen receptor positive), the authors of the recently published Women’s Healthy Eating and Living Study (121) write:

Our study is the third epidemiological study to report no adverse effects of soy foods on breast cancer prognosis. These studies, taken together, which vary in ethnic composition (two from the US and one from China) and by level and type of soy consumption, provide the necessary epidemiological evidence that clinicians no longer need to advise against soy consumption for women diagnosed with breast cancer.

Wartman cites the 2000 Honolulu-Asia Aging Study, saying that it linked soy with an increased risk of Alzheimer’s disease and brain shrinkage. Actually, this study does not mention Alzheimer’s Disease, although it did measure cognitive function. Let me sum up the evidence on soy and mental cognition.

There have been twelve short-term (lasting one week to a year) clinical trials looking at the impact of soy on cognition, and all have shown soy to be helpful (44, 45, 48, 49, 4750, 54, 55, 56) or neutral (51, 52, 57).

Epidemiological studies (unlike clinical trials), examine patterns of soy consumption and cognition in specific populations. One such study found tempeh (a fermented soy food) to be associated with improved cognition (9). Three reports from epidemiological studies have associated tofu with reduced cognition in some groups (2, 9, 53), but increased cognition in another group (42), and neutral in others (42, 53). The harmful findings for tofu in the epidemiological studies are likely due to confounding caused by the fact that people of lower economic status have traditionally eaten more tofu in Asian cultures as well as the fact that some tofu has been prepared using formaldehyde (at least in Indonesia from where some of these reports have come). The research as a whole provides little cause for concern.

Infant Formulas

Wartman suggests that soy-based infant formulas are “Perhaps the most alarming…” While I can understand the concern given that some infants are eating nothing but soy, the most important study to date, tracking adults who were fed soy formula as infants, provides assurance that there is no reason to be concerned about thyroid or reproductive function (95). Furthermore, the American Academy of Pediatrics and the National Toxicology Program considers soy formula safe.

The Beginnings Study is an ongoing study examining the effects of formula on child development (86). It is in its early stages with findings from children only a year old, but to date no negative effects of soy have been found on growth, sex organs, or neurological development compared to children on cow’s milk formula.

Some research shows that is best to choose a soy formula with DHA, and it is important to note that soy-formula is not intended for pre-term infants.

Feminizing Characteristics

Regarding the concern that soy could cause feminizing characteristics in men, there have been two case studies. In one, a man eating twelve servings per day of soymilk developed enlarged, sensitive breast tissue (123). In another, a man with type 1 diabetes was eating 14 servings per day of mostly processed soy foods for one year and developed erectile dysfunction (10), which normalized after ceasing the soy. While I would not recommend eating this much soy, one study used even much higher amounts of isoflavones and found no problems for most men (124).

As for sperm quantity and quality, while one epidemiological study raised concerns, albeit minor, about soy and sperm quantity (14), two clinical studies have shown no effects of soy (15, 126).

Thyroid

I do want to address one more issue that has recently arisen with the publishing of a clinical trial this year in which 16 mg/day of isoflavones in people with mild hypothyroidism appeared to cause an increased rate of advancing to overt hypothyroidism (78). Nine other clinical trials showed no effect of soy on the thyroid compared to placebo in people with presumably healthy thyroids (13, 60, 63, 64, 66, 68, 69, 71, 75) while the remaining five studies found small changes, all without physiological significance (61, 65, 70, 73, 74). People without hypothyroidism should have no problems with soy as long as they get enough iodine, but until we know more, people with mild hypothyroidism might want to avoid soy just to be safe.

In addition to reducing the risk for breast cancer as mentioned above, soy also provides benefits for preventing prostate cancer, lowering LDL cholesterol, and improving menopausal symptoms. When you add up all the research on soy, there is no reason to think that two servings per day are harmful to most people, and good reason to think soy will provide some health benefits.

This entry was posted on Tuesday, April 5th, 2011 at 9:00 am and is filed under Soy. You can follow any responses to this entry through the RSS 2.0 feed.
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Wonderful! I can’t wait to read this through carefully later. Thank you, Jack, for presenting this cutting edge synopsis of soy, and as always for ” trying to get to the truth rather than putting a positive spin on the results.” That’s why you are so trustworthy!

A quick aside: it is my understanding that none of the Field Roast products contain soy. So, true that they are free of hexane extracted soy but only because they contain no soy at all!

In the research discussed here, soy is typically described in grams of protein or milligrams of isoflavones. Less frequently, soy is described in grams of total soy foods. To make things more complicated, sometimes the participants in research are given only soy protein concentrate (about 65% protein), the isolated soy protein (about 90% protein), and sometimes only isolated isoflavones.

A rough guide is that one serving of soy equals 1 cup of soymilk, or 1/2 cup of tofu, tempeh, soybeans, or soy meats. This is the rough equivalent of about 8 to 10 grams of soy protein and 25 mg of isoflavones. The more processed soy meats tend to have more protein (but fewer isoflavones per gram of protein).

FYI the second reference to 123 under feminization and soy is a broken link.

[…] Jack Norris reviewed 130 papers over the course of 3 months in preparing his response to Wartman’s article. The editors of the “Civil Eats” blog decided not to publish it, but you can read that response here […]

In one, a man eating twelve servings per day of soymilk developed enlarged, sensitive breast tissue (123).

Going by what you wrote what a “serving” of soy may be, that would mean this guy would have had to drank 3/4 of a gallon of soy milk every day to make that happen.

If 1/2 cup of tofu is about ( roughly ) 1/4 of a 1 pound block of tofu, this man would have had to eat 3 blocks/packages of tofu a day.

According to nutritiondata.com a cup of frozen, cooked edamame ( fresh soy beans ) has 17 grams of protein which would make it about 2 servings of soy. So, this man would have had to been eating 6 cups of edamame a day to get his sickly dosage.

Since processed soy has even fewer isoflavones, the amounts would be even more ridiculously high.

The only people who I ever saw eat amounts of food like that were powerlifters I used to work out with in college.

I wonder if those two men ( out all of the others who haven’t had those problems ) began with compromised testosterone levels.

Regarding isoflavones and their potential estrogenic (and anti-estrogenic) effects, I find it quite amusing that such a fuss is made about soy while ignoring other edible plants that contain so-called phytoestrogens and, of course, the elephant in the room that is dairy containing real mammalian estrogens and other female sex hormones.

Question – Since two servings of soy per day are deemed healthy and beneficial, was there a clearer upper limit to soy servings per day where a significant number of people started having (any) problems? (And I don’t mean the folks eating 10-12+ servings a day, that seems excessive pretty much no matter what you’re eating.)
Because if you’re like me, and getting most of your daily calcium, B12 and vitamin D in two cups of soy milk, then the occasional tofu dog, grilled tofu or soy yogurt will put me at an average of about 2.5 – 3 servings a day, which I imagine, may be a common scenario for soy-eating vegans.

This is a legitimate and expected question, and one I considered pre-empting by addressing in the article. However, I do not like to surmise where there is not sufficient data (if I can avoid it!). A lot of the clinical trials used a lot more isoflavones than the equivalent of 2 servings per day and most did not have any problems with soy. I personally think there is a decent amount of evidence to suggest up to 4 servings is safe (if you do not have thyroid problems). But I would not say there is enough evidence to prove that to be the case. That is based on clinical trials, not epidemiological studies. In some ways, clinical trials are considered to be better evidence than epidemiological studies, but they are never as long term as some epidemiological studies. Until we have large numbers of people eating 3, 4, or 5 servings of soy per day for years at a time, it will be hard to know how much is really safe. If you want to know what I do, I eat about 3-4 servings a day – a glass of soymilk in the morning, some soy meats, tempeh, or tofu later in the day, and soy pudding for a bedtime snack. And I’m not worried about those amounts.

Hi Jack,
Thank you for all of your hard work! I’m a pregnant vegan and was just diagnosed with very mild hypothyroidism and put on a low dose of synthroid. I’ve been eating more soy since getting pregnant because it’s just an easier way to pack in the protein (almost always in the form of tofu or tempeh, very occasionally I have a glass of soy milk or a serving of soy meat at a restaurant). I’m probably eating 3-4 servings a day on average. I know that I get plenty of iodine in the form of iodized salt, some dulse flakes (for seasoning), and a daily prenatal vitamin. Would you still suggest I cut down or eliminate my soy consumption if my hypothyroidism is controlled with medication and I’m getting a lot of iodine? I’m working on using beans more to meet my protein needs, but struggling with pregnancy pickiness over food and beans aren’t as appetizing as they used to be.

Jack Norris RD wrote:
“I checked into how much estrogen was in dairy and it appears not not be a significant source.”

According to this source, dairy products “account for 60–70% of the estrogens consumed” (does this include xenoestrogens?): http://www.medical-hypotheses.com/article/S0306-9877%2801%2991380-5/abstract
I have no informed opinion on whether “animal-derived estrogens in the human diet” exert biologically significant effects. My point was that much fuss is made about so-called phytoestrogens (“so-called” because they are not plant estrogens in the literal sense), which happen to be much less potent than real estrogens and could therefore exert both estrogenic and anti-estrogenic effects, whereas no one seems to question the real estrogens in many people’s diets.
This is akin to obese men who meticulously avoid plastic bottles while the greatest threat to their male endocrine system lies in their belly fat.

Do any of these studies mention whether the soy being used is genetically engineered? Animal studies and clinical trials have linked GE foods to thyroid issues, immune responses, horizontal gene transfer and more. Not all soy is created equal.

If you were eating 3-4 servings of soy a day when your doctor tested you and put you on synthroid, then that dose should be appropriate for the amount of soy you are eating. But if you have added the soy since then, you should probably check with your doctor and possibly get retested.

Thanks for a very informative article Jack! I have been a vegan for 3 years and recently found out that I have hypothyroidism (tsh = 11). I am not sure if its genetic or because of soy (I have been eating about 2 servings of soy on average ever since I became vegan). I am currently taking thyroxine daily and so am wondering if I can continue to eat soy ?

My understanding, which is somewhat limited, is that it it okay to eat soy while taking thyroid hormone, but that if you change the amount you are eating, you should let your doctor know in case the medication amount needs to be adjusted.

I find all the worry and fuss about soy/thyroid issues funny and confusing at the same time. I used to worry about it having been hypothyroid for 30 years. I have taken the same dose (150 mcg) daily for 30 years. Since going vegan 2 years ago and adding 2-4 servings of soy per week my thyroid dose is now too high and I will have to take less medication now. I think people with thyroid issues are being scared away from soy unnecessarily.

[…] CivilEats is a great site, but they blew it by publishing “Not Soy Fast.” To protect their reputation and for the sake of not leading more of their readers astray they should waste no time in taking down Wartman’s now-discredited piece. Link. […]

I have not reviewed the literature on soy and IGF-1 and would not be surprised if soy protein does raise IGF-1 levels given that protein of any kind (and zinc) tends to raise IGF-1 levels. What is more important to me is whether that translates into an increased incidence of cancer. So, far the evidence is that soy protein does not increase the risk of cancer. I do not see why isolated soy protein would be different than soy protein in foods in this regard, assuming the amounts are similar.

Jack, are you saying plant foods like beans high in protein raise igf1 levels? Almost all the information I have found says that only dairy foods have the capability to raise igf1 significantly, as well as isolated soy protein.

There are many conflicting reports about igf 1 levels. Here’s an example.

I’m confused as to what to believe. Also do you risk eating something like isolated soy protein, something that isn’t a whole food to begin with? Shouldn’t we always choose the food that is whole when in doubt?

So if you go by that table, someone eating 4 regular slices of multi-grain bread per day (which weigh 26 g according to the USDA) would be eating about 4.7 mg of phytoestrogens. Whereas if you drink a glass of soymilk, you will be taking in 25 mg of isoflavones. Someone eating two or more servings of soy per day will dwarf the amount of phytoestrogens most Westerners eat.

Here are four studies, one from the US, one from Finland, and two from the Netherlands, which reported the average phytoestrogen intake to be 1 mg per day or less:

If someone eats a significant amount of flaxseeds, then their lignan intake will be significantly higher than non-soy eating Westerners (though hard to believe anywhere near someone eating 2-3 servings of soy per day).

> According to this source, dairy products “account for 60–70% of the estrogens consumed” (does this include xenoestrogens?):

I have no doubt that they do. But does that estrogen consumed raise estrogen levels? It doesn’t appear to. And here is something relevant from the CDC:

“Generally, phytoestrogens are much less potent than endogenously produced estrogens, but phytoestrogens can be present [in the body – JN] in much greater quantities (100 to 1000 times the concentration of endogenous estrogens).”

So, I stand by my view that the amount of phytoestrogens in soy have caused reasonable concern compared to the phytoestrogens, or real estrogens, in other foods.

> Jack, are you saying plant foods like beans high in protein raise igf1 levels?

I am saying that if you eat enough to consume about 20 to 25 grams of protein then, yes, they probably would increase IGF-1 levels. But, again, I haven’t reviewed the literature on that (at least in a long time).

Yes, there are conflicting reports about whether high IGF-1 levels increase the risk of cancer. I’d rather look at the direct evidence about whether a particular food causes cancer (if there is evidence available), and soy, in general, does not increase cancer.

> Shouldn’t we always choose the food that is whole when in doubt?

Seems like a good rule, but I am not in enough doubt to make it effect my food choices in this case.

“Whereas if you drink a glass of soymilk, you will be taking in 25 mg of isoflavones.”

May I ask how big your glasses are? According to the table, soy milk has got a phytoestrogen content of 2957.2 mcg/100g. 25 mg phytoestrogens (exclusively isoflavones?) would therefore be in about 845 g of such soy milk.

“‘Generally, phytoestrogens are much less potent than endogenously produced estrogens, but phytoestrogens can be present [in the body – JN] in much greater quantities (100 to 1000 times the concentration of endogenous estrogens).'”

I reckon the questionable usefulness of in vitro studies, but according to the following study, the potency of genistein, which appears to be one of the strongest phytoestrogens, is inversely much less than the general much greater quantity (“[…] genistein was four to six orders of magnitude less potent than 17beta-oestradiol […]”):

Some nutritionists are opposed to any non-traditional processed foods. And any industry that arises in an attempt to replace meat is going to incur a lot of criticism. Since soy meats fall into both of these categories, they are going to get a lot of criticism. And it probably doesn’t help that soy is especially high in phytoestrogens – both soy’s blessing and its curse.

> May I ask how big your glasses are? According to the table, soy milk has got a phytoestrogen content of 2957.2 mcg/100g. 25 mg phytoestrogens (exclusively isoflavones?) would therefore be in about 845 g of such soy milk.

I’m not sure why the chart you linked to lists soymilk as having only 3 mg isoflavones per 100 g. There are many ways to make soymilk and they might be using numbers from soymilk processed in a way that reduces the isoflavone content.

As for the connections between soy and feminizing characteristics, I also think it’s important to note a few other things.
so many people believe that soy reduces sperm count, although the research you cited shows that has little or no effect. Actually, there has been more connections found between sperm count, erectile dysfunction, etc. and meat than soy (http://www.holistichealthtools.com/viagra.html). even if soy has a little impact, it is better than its alternative of meat. (not to mention other health reasons, the environment, animal cruelty, etc.)

I do know what to look for when I have questions as to the effectiveness or “dangers” of a food/ item, and the other point is, “everything in moderation”. It boils down to each individual knowing their bodies, and what they may or may not eat. Self-research is the key.
What I find to be vexxing and ridiculous, at the same time, is how many non-vegetarians & non-vegans want to create myths about certain foods. It seems to me to be a childish retaliation – an Anthony Bourdain move, of sorts.

Thank you for this! I have gone to lectures and have had people tell me how bad soy is for me and that the Japanese ony eat tempeh and very little. I lived in Japan and travelled throughout Asia and know that this is not true. Japanese mainly eat tofu and its byproducts-yuba and they eat copious amounts of it. In Indonesia, they eat a lot of tempeh and tofu. They still tell me that I am wrong.
I do try to buy non GMO. People who protest against soy and eat factory farmed meat do not seem to realize that the animal flesh that they consume has been fed GMO corn.
I feel better after I have eaten tofu or tempeh.

Here is a link to an article John Robbins wrote about that subject. The Japanese Health Ministry ( can’t get more Asian than that ) decided to study the longevity of the Okinawan Islanders. They discovered that they ate a lot of soy, much more than “as a condiment”:

Here is a URL to a beverage industry article about soy drink consumption around the world. It contradicts what many people have been saying about Asians using soy in quantities so small that their soy use can only be considered as “condiments”.

Thanks Jack, for researching this issue and sharing. Valuable information on soy for those of us who don’t easily understand how to interpret the studies or don’t want to invest the time in doing the research.

Good morning ! This article is interesting, nevertheless I feel that the persons who perform the studies, or write various articles about the subject : Influence of soy over breast cancer, are not personally concerned by the illness or don’t feel concerned with the risk of breast cancer. It happens that I was operated of this cancer, 9 months chimo, 43 sequences of radiotherapy, and I can tell you that I will not take the risk at all of eating soy anymore, except fermented soy which properties are different from the fresh tofu or soy grains. Do you know that we can never completely get rid of cancer cells ? Do you know that everyday of my life I am at risk ?
My Chinese Uncle told me that Chinese people do not eat soy every day, but more often Soya sauce, miso, or tempeh. Soya grains or milk must be eaten from time to time only since they represent a risk for the kidneys. Don’t give soy milk to babies or young children.
Anyway, thank you very much for your article, thank you very much for this site which a support for those who are trying to find a way for better health. With best regards.

> except fermented soy which properties are different from the fresh tofu or soy grains.

There may be some differences in properties, but, to my knowledge, there are no differences in the isoflavone content, and it’s the isoflavones that are the cause for concern regarding soy and breast cancer.

Thanks for the kind words. I can definitely see being extremely cautious regarding soy if you have breast cancer, but I am skeptical that being personally afflicted with breast cancer will change a researcher’s findings about the safety of soy.

If you’re still monitoring this discussion, then I wanted to say thank you. I have your book, which I admittedly have not finished yet, but I have been moving towards a vegan diet for a little over two weeks.

Some of my struggles have been with feeling extremely hungry not very long after eating large vegan meals (I also have the “Veganomicon” cook book). I have found that soymilk seems to really help with this, and I’m pretty sure the large glasses I’m consuming, along with some soy products at night would bring me to a much higher serving count than 3-4 a day. Probably closer to 5-7 a day.

I also give my son some soymilk each afternoon and night in his bottle (usually mixed in with coconut milk).

So, my concerns are:

1. Am I at a “dangerous” level for soy? I really love soy milk, so I’m hoping I’m OK. Roughly 3 large glasses or so.

2. My son being 2.5 years old is obviously much smaller than me, but it is one of the few ways I can get him to get some protein (he actually never has been a big meat eater, we always had to mix it in to something). Am I putting him at risk with a serving count of 2-3 (depending on whether he’s had a tofurkey dog that night)?

I would try to eat less than 5-7 servings of soy per day. What do you eat for fat? My experience with not feeling satisfied is that its either not enough protein, fat, or calories. Have you been losing any weight? If not, then you’re probably getting enough calories and. So I would move on to fat or protein, both of which are provided by most soyfoods. There, of course, many other sources of both and I don’t know what you’ve tried. A serving or 2 of seitan (which is made from wheat, not soy) might be a way to get a lot of protein without eating soy. And there are many other legumes, of course – peanut butter, refried beans, etc.

As for your son, if he won’t eat other sources of protein, then I guess soy milk is a decent option, though I don’t know how much you are feeding him.

I actually have lost a couple of pounds, so my weight is OK, and I could stand to lose some more, but that’s another matter. Yesterday I ate a huge serving of a recipe that included beans and TVP (again, I guess, soy), and I felt so satiated the rest of the night. First time in a while.

I have only gone up to the higher soy serving count one or two days, so perhaps I was exaggerating a bit. , and you’re right on the legumes. Some of my issues have stemmed from not preparing enough, which is new to me. I will look into seitan and try to vary things up some more. Again, thanks, and thanks for your book. I’m going to re-read the soy section and this article and see if I can do a bit better.

RESULT(S): In contrast to the results of some rodent studies, findings from a recently published metaanalysis and subsequently published studies show that neither isoflavone supplements nor isoflavone-rich soy affect total or free testosterone (T) levels. Similarly, there is essentially no evidence from the nine identified clinical studies that isoflavone exposure affects circulating estrogen levels in men. Clinical evidence also indicates that isoflavones have no effect on sperm or semen parameters, although only three intervention studies were identified and none were longer than 3 months in duration. Finally, findings from animal studies suggesting that isoflavones increase the risk of erectile dysfunction are not applicable to men, because of differences in isoflavone metabolism between rodents and humans and the excessively high amount of isoflavones to which the animals were exposed.

CONCLUSION(S): The intervention data indicate that isoflavones do not exert feminizing effects on men at intake levels equal to and even considerably higher than are typical for Asian males. Copyright 2010. Published by Elsevier Inc. ”

Abstract
Semen specimens (one ejaculate from each of 20 consenting study participants) were subjected to routine semen analysis, an in vitro sperm binding assay (HBA), and a sperm chromatin dispersion assay (HaloSperm), both before and after cryopreservation using cryoprotectant media supplemented with either egg yolk or soy lecithin. Comparing the equivalency of the two phospholipid cryopreservation supplements with regard to postthaw functional parameters demonstrated that there were no statistically significant differences between the two supplements for [1] recovery of motile sperm, [2] maintenance of sperm cell morphology, [3] maintenance of the ability of sperm to bind to hyaluronate in vitro, or [4] maintenance of sperm DNA integrity.